# Increased Brain Glutathione Levels by Intranasal Insulin Administration

## TL;DR

Intranasal insulin increases brain antioxidants, which may help protect against brain diseases.

## Contribution

Intranasal insulin boosts brain glutathione via EAAC1 upregulation and reduced AMPK activation.

## Key findings

- Insulin-treated mice had higher GSH levels in the hippocampus and midbrain.
- EAAC1 expression increased in brain fractions of insulin-treated mice.
- AMPK activation and EAAC1-GTRAP3-18 interaction were reduced with insulin.

## Abstract

Background: This paper investigates the effect of intranasal insulin administration on brain glutathione (GSH) levels and elucidates the potential mechanism by which insulin enhances antioxidant defenses in the brain. Methods: C57BL/6J mice were intranasally administered insulin (2 IU/day) or saline for 7 days. GSH levels were measured in the brain and liver. Blood glucose concentrations and daily food intake were also monitored. Protein levels of excitatory amino acid carrier-1 (EAAC1), its interaction with glutamate transport-associated protein 3-18(GTRAP3-18), and activated AMP-activated protein kinase (AMPK) were assessed. Results: Insulin-treated mice exhibited significantly higher GSH levels in the hippocampus and midbrain compared to saline-treated controls, while no significant differences were found in liver GSH levels, blood glucose concentrations, or food intake. EAAC1 expression increased in both the cytosolic and plasma membrane fractions of insulin-treated mouse brains. Furthermore, the interaction between EAAC1 and its negative regulator, GTRAP3-18, along with activated AMPK levels, was reduced in insulin-treated mice. Conclusions: Intranasal insulin administration enhances brain GSH levels through a mechanism involving EAAC1 upregulation and reduced AMPK activation. These findings suggest that intranasal insulin could be a promising strategy for enhancing antioxidant defenses against neurodegeneration in the brain.